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Comparison of Maximum Permissible Activity of I-131 Determined by Benua and Leeper Method and Blood Absorbed Dose Method in Differentiated Thyroid Carcinoma Patients |
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PP: 45-49 |
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doi:10.18576/jrna/070206
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Author(s) |
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Touqir Ahmed Afridi,
Muhammad Waqar,
Ambreen Khawar,
Naureen Marwat,
Zubair Ahmed Soomro,
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Abstract |
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| Background: Iodine-131 NaI is the mainstay of treatment in patients with well differentiated carcinoma. Fixed versus dosimetrically determined doses for iodine therapy are long in debate. Objectives: In this study, two dosimetry methods for the calculation of maximum tolerable activity (MTA) of iodine-131 NaI for treatment of well-differentiated thyroid carcinoma patients were compared. Materials & Methods: The methods included blood dosimetry method based on the Medical and Internal Radiation Dosimetry (MIRD) and 48-hour retention limit method based on modified Benua and Leeper method. For dosimetric analysis whole-body scans were obtained using pre-calibrated dual head SPECT/CT gamma camera for I-131 along with 1 ml blood samples at 2, 24, and 48 h post administration of I-131. Percent activity uptake in whole body as well as blood samples were determined. MATLAB was used to generate time activity curves and to calculate cumulative activities for whole body and blood at all-time points. Using the published MIRD formalism radiation absorbed dose to blood was determined. For 48-h retention limit method, percent whole body retention activities at 2, 24, and 48 h were plotted against time to fit Bi-Exponential curve. MTA with blood dosimetry method was calculated by dividing 2 Gy absorbed dose limit to blood. MTA with 48 h retention method was calculated by using 4.4 GBq retention limit at 48 h in Bi-Exponential decay equation. Results & Discussion: The MTA range with blood dosimetry method was found to be 395 mCi to 923 mCi as compared to 894.6 mCi to 4490 mCi with 48-hour retention method. Higher estimation of MTA is consequent to low retention of I-131 as none of the patients had any residual/metastatic disease. Conclusions: For lower retentions at 48 hours (<5%), the MTA differed up to the factor of 5. However, for the retention of up to 10%, MTA differed by the factor of 3. Hence, 48-hour retention limit method was found to over-estimate the MTA as compared to blood dosimetry method. |
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